1. Field of the Invention
The present invention relates to a clock spring connector for use with a steering device of an automobile, for example, including a fixed member, a movable member, and a cable for effecting electrical connection between the fixed member and the movable member.
2. Description of Related Art
A clock spring connector is generally constructed of a fixed member, a movable member rotatably mounted on the fixed member, a flexible cable connecting the fixed member and the movable member. Such a clock spring connector is used as an electrical connecting device for effecting electrical connection between the fixed member and the movable member adapted to be rotated with a finite number of revolutions as in a steering device of an automobile.
In a known clock spring connector of this kind, a cable accommodating portion is defined between the fixed member and the movable member, and a flat cable formed by laminating a pair of strip films with a plurality of conductors sandwiched therebetween is loosely accommodated in the cable accommodating portion under a spirally wrapped condition. One end of the flat cable is fixed to an outer cylindrical portion formed on either the fixed member or the movable member, while the other end of the flat cable is fixed to an inner cylindrical portion formed on the other of the fixed member and the movable member.
When the movable member of the clock spring connector is rotated, the flat cable accommodated in the cable accommodating portion can be wrapped onto the inner cylindrical portion from the outer cylindrical portion or unwrapped from the inner cylindrical portion to the outer cylindrical portion according to a rotational direction of the movable member. Accordingly, while the flat cable is being unwrapped from the inner cylindrical portion to the outer cylindrical portion, almost no tension is applied to the flat cable, and electrical connection between the fixed member and the movable member rotating relative thereto can be maintained at all times.
The wrapping and unwrapping of the flat cable is carried out by utilizing a difference in diameter between the outer cylindrical portion and the inner cylindrical portion. Therefore, assuming that a rotational amount of the movable member is fixed, the larger the difference in diameter, the smaller the length of a flat cable that is necessary. However, the diameter of the inner cylindrical portion is dependent upon a diameter of a rotating shaft on which the clock spring connector is mounted, e.g., a steering shaft of an automobile. On the other hand, the diameter of the outer cylindrical portion cannot be made too large because a compact size of the clock spring connector is desirable. For these reasons, the difference in diameter between the outer cylindrical portion and the inner cylindrical portion cannot be made extremely large. Accordingly, such a clock spring connector generally requires a long flat cable, which is difficult to manufacture as is well known. As a result, a total cost of the clock spring connector is increased.